1. Field of the Invention
This invention relates to a system for measuring the magnitude of a load connected to a drive shaft.
2. Description of the Prior Art
A conventional system for measuring the magnitude of a load connected to the drive shaft of a motor includes a torsion bar connected between the drive shaft and the driven rotary shaft of the load, and a pair of sensors, one of which is provided on the drive shaft-side of the torsion bar and the other of which is provided on the rotary shaft-side thereof, for sensing the rotational position of the shaft on each side. The magnitude of the applied load is measured based on the difference between the rotational positions of the shafts sensed by the respective sensors.
An example of the conventional apparatus for measuring the magnitude of the load is illustrated in FIG. 1. A pulse motor 1 rotates a drive shaft 1a on the driving side. A load 2 on the driven side is the object whose load is to be measured and has a rotary shaft 2a. A torsion bar 3 connects the shaft 1a with the shaft 2a. Discs 4 and 5, each having slits formed in the outer peripheral portion thereof, are fixed to the torsion bar 3 for co-rotation therewith. A sensor A comprises light-emitting and light-receiving elements 6a, 6b arranged to oppose each other across the disc 4. Similarly, a sensor B comprises light-emitting and light-receiving elements 7a, 7b arranged to oppose each other across the disc 5. The set-up is such that when a beam of light from the light-emitting element 6a impinges upon the light-receiving element 6b by passing through a slit in the disc 4, or when the light beam is interrupted by a non-transmissive portion of the disc, as the disc rotates, this is sensed by the sensor A which, in response, produces an output signal. In like manner, the sensor B produces an output signal as the disc 5 rotates. The load torque on the driven side is measured based on the phase difference between the two output signals.
With this conventional arrangement, sensing mechanisms must be provided on the active and passive sides, the amount of rotation on each side must be sensed, and a plurality of sensing points are essential. The result is a structure of some complexity. In addition, sensors on the active and passive sides must be corrected for any error in the rotation, and a great deal of time is consumed for such tasks as adjusting the positions at which the sensing mechanisms are mounted. U.S. Pat. No. 3,495,452 to Johnson, Jr. et al. and U.S. Pat. No. 3,564,909 to Foskett et. al. are inventions designed to arrange two discs in adjacent positions to simplify the adjustment of the positions of the sensing mechanisms. In these patents, two discs are provided, one on each end of the torsion bar, so the adjustment of the positions of the disc and the high cost entailed in the necessity to provide a plurality of the sensing mechanisms cannot be avoided.